Various processes and devices have been developed for incinerating solid particulate materials for various purposes. In particular, municipal waste and sewer sludge generally must be incinerated before disposal in a landfill. The environmental regulations in many countries limit the amount of organic material which can be present in the sludge prior to disposal. Accordingly, various efforts have been proposed to incinerate municipal waste material and sewer sludge to comply with the regulations.
One example of a known process for incinerating waste materials is disclosed in WO 92/14969. This publication discloses a process for feeding finely ground, previously dried sludge into a brick lined combustion chamber, together with a supply of primary combustion air. The furnace is a cyclone combustion chamber having a lower section where the incineration of the solid material takes place. A predetermined amount of moist air with a reduced oxygen content is fed into the combustion chamber to inhibit the sintering of the ash. The ash discharge area of the combustion chamber is cooled using the moist air. The amount of air needed as the primary combustion air and the secondary source of moist air is typically preset for a specific furnace size. The heat output of the furnace is regulated by adjusting the amount of the solid material being incinerated in relation to the fixed amount of the primary combustion air. This device has several disadvantages and is not completely efficient in incinerating solid materials. For example, the process disclosed in this publication is generally difficult to regulate and the output of the incinerated material can be adjusted over a very small operating range. Furthermore, fluctuations in the level of solid material being incinerated and the caloric value of the solid material produces inconsistent results in the incineration of the solid material.
Accordingly, there is a continuing need in the industry for improved processes and apparatus for incinerating solid materials.